U.S. patent application number 16/269271 was filed with the patent office on 2019-06-06 for antireflection film, optical element, optical system, method of producing antireflection film.
This patent application is currently assigned to FUJIFILM Corporation. The applicant listed for this patent is FUJIFILM Corporation. Invention is credited to Yuichiro ITAI, Seigo NAKAMURA, Kenichi UMEDA, Hideki YASUDA.
Application Number | 20190170908 16/269271 |
Document ID | / |
Family ID | 61309138 |
Filed Date | 2019-06-06 |
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United States Patent
Application |
20190170908 |
Kind Code |
A1 |
UMEDA; Kenichi ; et
al. |
June 6, 2019 |
ANTIREFLECTION FILM, OPTICAL ELEMENT, OPTICAL SYSTEM, METHOD OF
PRODUCING ANTIREFLECTION FILM
Abstract
An antireflection film is formed by laminating an interlayer, a
silver-containing metal layer containing silver, and a dielectric
layer in this order from the substrate, an anchor region including
an oxide of an anchor metal is provided between the
silver-containing metal layer and the interlayer, a cap region
including an oxide of the anchor metal included in the anchor
region is provided between the silver-containing metal layer and
the dielectric layer, a crystal grain size obtained by X-ray
diffraction measurement in the silver-containing metal layer is
less than 6.8 nm, and the anchor metal has a surface energy less
than a surface energy of silver and greater than a surface energy
of a layer of the interlayer closest to the silver-containing metal
layer.
Inventors: |
UMEDA; Kenichi; (Kanagawa,
JP) ; NAKAMURA; Seigo; (Kanagawa, JP) ; ITAI;
Yuichiro; (Kanagawa, JP) ; YASUDA; Hideki;
(Kanagawa, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FUJIFILM Corporation |
Tokyo |
|
JP |
|
|
Assignee: |
FUJIFILM Corporation
Tokyo
JP
|
Family ID: |
61309138 |
Appl. No.: |
16/269271 |
Filed: |
February 6, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP2017/031034 |
Aug 29, 2017 |
|
|
|
16269271 |
|
|
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 15/20 20130101;
B32B 15/04 20130101; C23C 14/5893 20130101; G02B 1/116 20130101;
C23C 14/06 20130101; C23C 14/14 20130101; G02B 15/167 20130101;
G02B 1/115 20130101; B32B 9/00 20130101; C23C 14/024 20130101 |
International
Class: |
G02B 1/115 20060101
G02B001/115 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 31, 2016 |
JP |
2016-168900 |
Claims
1. An antireflection film that is provided on a substrate and is
formed by laminating an interlayer, a silver-containing metal layer
containing silver, and a dielectric layer in this order from the
substrate, comprising: an anchor region including an oxide of an
anchor metal provided between the silver-containing metal layer and
the interlayer; and a cap region including an oxide of the anchor
metal provided between the silver-containing metal layer and the
dielectric layer, wherein a crystal grain size obtained by X-ray
diffraction measurement in the silver-containing metal layer is
less than 6.8 nm, and the anchor metal has a surface energy less
than a surface energy of silver and greater than a surface energy
of a layer of the interlayer closest to the silver-containing metal
layer.
2. The antireflection film according to claim 1, wherein a total
film thickness including the anchor region, the silver-containing
metal layer, and the cap region is 10 nm or less.
3. The antireflection film according to claim 1, wherein the anchor
region includes the anchor metal which is not oxidized, and a
content ratio of the oxide of the anchor metal is larger than a
content ratio of the anchor metal which is not oxidized.
4. The antireflection film according to claim 1, wherein the anchor
metal is formed of Ge, Sn, In, Ga, Zn, Bi, Pb, Mg or Si.
5. The antireflection film according to claim 1, wherein the anchor
metal is formed of Ge, Sn, In, or Ga.
6. The antireflection film according to claim 1, wherein the
surface energy of the anchor metal is 350 mN/m or more and 1000
mN/m or less.
7. The antireflection film according to claim 1, wherein the
surface energy of the anchor metal is 500 mN/m or more and 900 mN/m
or less.
8. An optical element comprising: the antireflection film according
to claim 1.
9. An optical system comprising: a group lens in which the
antireflection film of the optical element according to claim 8 is
arranged on outermost surfaces thereof.
10. A method of producing an antireflection film, the
antireflection film being provided on a surface of a substrate, the
method comprising: forming an interlayer, an anchor layer formed of
an anchor metal, and a silver-containing metal layer containing
silver, in this order, on the surface of the substrate; annealing
the substrate on which the interlayer, the anchor layer, and the
silver-containing metal layer are laminated, in ambient air;
forming a dielectric layer on cap region, which is an outermost
surface of a laminate obtained by the annealing, the laminate
comprising an anchor region including an oxide of the anchor metal
provided between the silver-containing metal layer and the
interlayer, and the cap region including an oxide of the anchor
metal formed at a surface thereof, wherein a crystal grain size
obtained by X-ray diffraction measurement in the silver-containing
metal layer is less than 6.8 nm.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation application of
International Application No. PCT/JP2017/031034, filed Aug. 29,
2017, the disclosure of which is incorporated herein by reference
in its entirety. Further, this application claims priority from
Japanese Patent Application No. 2016-168900, filed Aug. 31, 2016,
the disclosure of which is incorporated herein by reference in its
entirety.
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0002] The present invention relates to an antireflection film, an
optical element including an antireflection film, and an optical
system including the optical element.
2. Description of the Related Art
[0003] In the related art, in a lens (transparent substrate) formed
of a light transmitting member such as glass or a plastic, an
antireflection film is provided on a light incident surface in
order to reduce the loss of transmitted light caused by surface
reflection.
[0004] As an antireflection film that exhibits a very low
reflectance with respect to visible light, configurations of a fine
uneven structure having a pitch shorter than the wavelength of
visible light and a porous structure obtained by forming a large
number of pores on the uppermost layer thereof are known. In a case
of using an antireflection film having a structure layer of a fine
uneven structure, a porous structure, or the like on the uppermost
layer as a layer of low refractive index, an ultra-low reflectance
of 0.2% or less can be obtained in a wide wavelength range of a
visible light region. However, since these films have a fine
structure on the surface thereof, there are defects that the film
has low mechanical strength and is very weak to an external force
such as wiping. Therefore, portions such as outermost surfaces
(first lens front surface and final lens back surface) of a group
lens used for a camera lens or the like, which are touched by a
user, cannot be subjected to ultra-low reflectance coating having a
structure layer.
[0005] On the other hand, as an antireflection film not including a
structure layer on the surface thereof, an antireflection film
including a metal layer containing silver (Ag) in a laminate of
dielectric films is disclosed in JP2006-184849A, JP1996-054507A
(JP-H08-054507A), JP2003-255105A, and the like.
[0006] JP2006-184849A discloses an antireflection laminate having a
conductive antireflection layer obtained by alternately providing a
high refractive index transparent thin film layer and a metal thin
film layer on a transparent substrate, and a low refractive index
transparent thin film layer in contact with the high refractive
index transparent thin film layer on the outermost layer thereof.
In addition, JP2006-184849A discloses that as a layer for
protection from corrosion, a protective layer may be provided for
upper and lower layers of the metal thin film layer. For the
protective layer, metals such as zinc, silicon, nickel, chromium,
gold, and platinum, alloys thereof, and oxides, fluorides, sulfides
and nitrides of these metals may be used.
[0007] JP1996-054507A (JP-H08-054507A) discloses an antireflection
film including a thin metal layer that is interposed between a
front coating layer and a back coating layer and is protected from
scratches by a protective silicon nitride layer. For the coating
layers, nickel, chromium, rhodium, platinum, tungsten, molybdenum,
tantalum, an alloy of nickel and chromium, and the like may be
used.
[0008] JP2003-255105A discloses an antireflection film that is
formed by laminating a metal thin film layer and a metal oxide thin
film layer on a substrate, in which an underlayer is provided
between the substrate and the metal thin film layer in order to
stabilize the metal thin film layer, and an interlayer is provided
between the metal thin film layer and the metal oxide thin film
layer. As the underlayer and the interlayer, metal thin film layers
of silicon, titanium, and the like may be used.
SUMMARY OF THE INVENTION
[0009] However, in a case where a metal layer is provided as a
protective layer or a coating layer on the upper and lower layers
of the metal thin film as disclosed in JP2006-184849A,
JP1996-054507A (JP-H08-054507A), and JP2003-255105A, there is a
problem that transparency is lowered due to coloration with a
metal. Further, in a case where an oxide or a nitride is provided
as disclosed in JP2006-184849A, the surface energy is small, and
thus, in a case where an extremely thin metal thin film layer is
formed thereon, aggregation of the metal occurs so that the metal
is granulated. Thus, it is difficult to form a flat film.
Therefore, it is not possible to achieve both high transparency and
high flatness, and antireflection performance may be lowered.
[0010] The present invention is made in consideration of the above
circumstances, and an object thereof is to provide an
antireflection film having high mechanical strength, high light
transmittance, and high antireflection performance, an optical
element including the antireflection film, and an optical system
including the optical element.
[0011] According to the present invention, there is provided an
antireflection film that is provided on a substrate, and is formed
by laminating an interlayer, a silver-containing metal layer
containing silver, and a dielectric layer in this order from the
substrate, comprising:
[0012] an anchor region including an oxide of an anchor metal
provided between the silver-containing metal layer and the
interlayer; and
[0013] a cap region including an oxide of the anchor metal provided
between the silver-containing metal layer and the dielectric
layer,
[0014] in which a crystal grain size obtained by X-ray diffraction
measurement in the silver-containing metal layer is less than 6.8
nm, and
[0015] the anchor metal has a surface energy less than a surface
energy of silver and greater than a surface energy of a layer of
the interlayer closest to the silver-containing metal layer.
[0016] Here, the expression "containing silver" indicates that the
content of silver included in the silver-containing metal layer is
50 atomic % or more.
[0017] Here, the expression "crystal grain size obtained by X-ray
diffraction measurement" refers to a value obtained by acquiring an
X-ray diffraction chart by grazing incidence X-ray diffraction
(GIXRD) which is measurement for a thin film with the incidence
angle fixed near the critical angle, and calculating the value from
a half-width of a (111) plane peak of silver observed near a
diffraction angle 2.theta.=38.degree. in the X-ray diffraction
chart using the Scherrer equation.
[0018] In the antireflection film of the present invention, it is
preferable that a total film thickness including the anchor region,
the silver-containing metal layer, and the cap region is 10 nm or
less.
[0019] In the antireflection film of the present invention, it is
preferable that in a case where the anchor region includes the
anchor metal which is not oxidized, a content ratio of the oxide of
the anchor metal is larger than a content ratio of the anchor metal
which is not oxidized.
[0020] In the antireflection film of the present invention, it is
preferable that the anchor metal is Ge, Sn, In, Ga, or Zn.
[0021] In the antireflection film of the present invention, the
surface energy of the anchor metal is preferably 350 mN/m or more
and 1000 mN/m or less and more preferably 500 mN/m or more and 900
mN/m or less.
[0022] According to the present invention, there is provided an
optical element comprising the antireflection film according to the
present invention.
[0023] According to the present invention, there is provided an
optical system comprising: a group lens in which the antireflection
film of the optical element according to the present invention is
arranged on outermost surfaces thereof.
[0024] Here, the expression "outermost surfaces" refers to one side
surfaces of lenses arranged at both ends of the group lens
consisting of a plurality of lenses and refer to surfaces which
become both end surfaces of the group lens.
[0025] The antireflection film according to the present invention
is formed by laminating an interlayer, a silver-containing metal
layer containing silver, and a dielectric layer on a substrate in
this order, in which an anchor region including an oxide of an
anchor metal is provided between the silver-containing metal layer
and the interlayer, a cap region including an oxide of the anchor
metal included in the anchor region is provided between the
silver-containing metal layer and the dielectric layer, a crystal
grain size obtained by X-ray diffraction measurement in the
silver-containing metal layer is less than 6.8 nm, and the anchor
metal has a surface energy less than a surface energy of silver and
greater than a surface energy of a layer of the interlayer closest
to the silver-containing metal layer. In the configuration, the
silver-containing metal layer has very high smoothness, and thus it
is possible to obtain a configuration having high antireflection
performance due to an antireflection structure in which the
interlayer and the dielectric layer are combined with the
silver-containing metal layer having high smoothness. Since the
anchor region and the cap region include an oxide of the anchor
metal, high transparency is obtained compared to a case where an
anchor layer formed of a metal is provided.
[0026] Since the antireflection film according to the present
invention does not have an uneven structure or a porous structure,
the antireflection film has high mechanical strength and is
applicable to a surface of an optical member which is touched by a
hand of a user.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a schematic cross-sectional view showing a
schematic configuration of an optical element including an
antireflection film according to an embodiment of the present
invention.
[0028] FIG. 2 is a diagram showing a production step of the
antireflection film.
[0029] FIG. 3 is a diagram showing a configuration of an optical
system consisting of a group lens including the optical element of
the present invention.
[0030] FIG. 4 is a diagram showing an element distribution of a
sample in Example 1 in a depth direction before annealing.
[0031] FIG. 5 is a diagram showing an element distribution of the
sample in Example 1 in the depth direction after annealing.
[0032] FIG. 6 is a diagram showing a Ge3d spectrum of the sample in
Example 1 in the depth direction before annealing.
[0033] FIG. 7 is a diagram showing a Ge3d spectrum of the sample in
Example 1 in the depth direction after annealing.
[0034] FIG. 8 is a scanning transmission electron microscope image
of the sample in Example 1.
[0035] FIG. 9 is a diagram showing an element distribution of the
sample in Example 1 in the depth direction by energy dispersive
X-ray spectrometry.
[0036] FIG. 10 is a diagram showing wavelength dependence of the
reflectance of an antireflection film in Example 7.
[0037] FIG. 11 is a diagram showing the reflection spectra of a
silver film in Preparation Example 1 and a silver alloy film in
Preparation Example 2 and the reflection spectrum of a silver film
obtained by simulation.
[0038] FIG. 12 is a scanning electron microscope image of the
silver film in Preparation Example 1.
[0039] FIG. 13 is a scanning electron microscope image of the
silver alloy film in Preparation Example 2.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0040] Hereinafter, embodiments of the present invention will be
described.
[0041] FIG. 1 is a schematic cross-sectional view showing a
schematic configuration of an optical element 10 including an
antireflection film 1 according to a first embodiment of the
present invention. As shown in FIG. 1, the antireflection film 1 of
the embodiment is formed by laminating an interlayer 3, a
silver-containing metal layer 4 containing silver (Ag), and a
dielectric layer 5 on a substrate 2 in this order. In the
antireflection film 1, an anchor region 7 including an oxide of an
anchor metal is provided between the silver-containing metal layer
4 and the interlayer 3, a crystal grain size obtained by X-ray
diffraction measurement in the silver-containing metal layer is
less than 6.8 nm, and a cap region 9 including an oxide of the
anchor metal is provided between the silver-containing metal layer
4 and the dielectric layer 5. Here, the anchor metal has a surface
energy less than a surface energy of silver and greater than a
surface energy of a layer of the interlayer 3 closest to the
silver-containing metal layer 4.
[0042] In the antireflection film 1 according to the embodiment of
the present invention, light to be reflected varies depending on
the purpose and is generally light in a visible light region. As
required, light in an infrared region may be used.
[0043] The shape of the substrate 2 is not particularly limited and
the substrate is a transparent optical member (transparent
substrate) that is mainly used in an optical device such as a flat
plate, a concave lens, or a convex lens and also may be a substrate
constituted by a combination of a curved surface having a positive
or negative curvature and a flat surface. As the material for the
substrate 2, glass, plastic, and the like can be used. Here, the
term "transparent" means being transparent (having an internal
transmittance of about 10% or more) to a wavelength of light of
which reflection is to be suppressed (reflection prevention target
light) in the optical member.
[0044] The refractive index of the substrate 2 is not particularly
limited and is preferably 1.45 or more. The refractive index of the
substrate 2 may be 1.61 or more and 1.74 or more and further 1.84
or more. For example, the substrate 2 may be a high power lens such
as a first lens of a group lens of a camera or the like. In the
present specification, the refractive index indicates a refractive
index with respect to light having a wavelength of 500 nm.
[0045] The interlayer 3 may be a single layer or may be formed of a
plurality of layers. In a case where the interlayer is a single
layer, the interlayer may have a refractive index different from
the refractive index of the substrate 2 and in a case where the
interlayer is formed of a plurality of layers, the interlayer is
preferably formed by alternately laminating a layer 11 of high
refractive index and a layer 12 of low refractive index. In this
case, as shown in (a) of FIG. 1, the layer 12 of low refractive
index and the layer 11 of high refractive index may be laminated in
this order from the substrate 2. As shown in (b) of FIG. 1, the
layer 11 of high refractive index and the layer 12 of low
refractive index may be laminated in this order from the substrate
2. In addition, the number of layers of the interlayer 3 is not
limited, but is preferably set to 16 layers or less from the
viewpoint of suppressing costs. The layer of the interlayer 3
closest to the silver-containing metal layer 4 means, in a case
where the interlayer 3 is a single layer, the layer itself.
[0046] The refractive index of the layer 11 of high refractive
index may be higher than the refractive index of the layer 12 of
low refractive index, and the refractive index of the layer 12 of
low refractive index may be lower than the refractive index of the
layer 11 of high refractive index. It is more preferable that the
refractive index of the layer 11 of high refractive index is higher
than the refractive index of the substrate 2 and the refractive
index of the layer 12 of low refractive index is lower than the
refractive index of the substrate 2.
[0047] The layers 11 of high refractive index, or the layers 12 of
low refractive index may not have the same refractive index.
However, it is preferable that the layers are formed of the same
material and have the same refractive index from the viewpoint of
suppressing material costs, film formation costs, and the like.
[0048] Examples of the material for forming the layer 12 of low
refractive index include silicon oxide (SiO.sub.2), silicon
oxynitride (SiON), gallium oxide (Ga.sub.2O.sub.3), aluminum oxide
(Al.sub.2O.sub.3), lanthanum oxide (La.sub.2O.sub.3), lanthanum
fluoride (LaF.sub.3), magnesium fluoride (MgF.sub.2), and sodium
aluminum fluoride (Na.sub.3AlF.sub.6).
[0049] Examples of the material for forming the layer 11 of high
refractive index include niobium pentoxide (Nb.sub.2O.sub.5),
titanium oxide (TiO.sub.2), zirconium oxide (ZrO.sub.2), tantalum
pentoxide (Ta.sub.2O.sub.5), silicon oxynitride (SiON), silicon
nitride (Si.sub.3N.sub.4), and silicon niobium oxide (SiNbO).
[0050] The refractive index can be changed to some extent by
controlling any of these compounds to have the constitutional
element ratio which is shifted from the compositional ratio of the
stoichiometric ratio or by forming a film by controlling the film
formation density. The materials constituting the low refractive
index and the high refractive index layer are not limited to the
above compounds as long as the above refractive index conditions
are satisfied. Further, unavoidable impurities may be included.
[0051] Each layer of the interlayer 3 is preferably formed by using
a vapor phase film formation method such as vacuum deposition,
plasma sputtering, electron cyclotron sputtering, or ion plating.
According to the vapor phase film formation method, a laminated
structure having various refractive indexes and layer thicknesses
can be easily formed.
[0052] The silver-containing metal layer 4 is a layer formed of 50
atomic % or more of silver with respect to the constitutional
elements. The layer may contain at least one of palladium (Pd),
copper (Cu), gold (Au), neodymium (Nd), samarium (Sm), bismuth
(Bi), platinum (Pt), tin (Sn), aluminum (Al), zinc (Zn), magnesium
(Mg), indium (In), gallium (Ga), or lead (Pb), in addition to
silver. Specifically, for example, as the material constituting the
silver-containing metal layer 4, an Ag--Nd--Cu alloy, an Ag--Pd--Cu
alloy, an Ag--Bi--Nd alloy, or the like may be suitably used. Since
the silver-containing metal layer 4 is formed as a very thin layer
whose design film thickness is preferably 6 nm or less, atom
migration occurs between the layers arranged above and below and
the composition at formation and the actual composition are
different.
[0053] As the raw material for forming the silver-containing metal
layer 4, a material in which 85 atomic % or more of the
constitutional elements is silver is preferably used. In this case,
the content of metal elements other than silver may be less than 15
atomic %, but is more preferably 5 atomic % or less and even more
preferably 2 atomic % or less. In this case, the content refers to
a total content of two or more metal elements in a case in which
the metal layer contains two or more metal elements other than
silver. From the viewpoint of preventing reflection, it is most
preferable to use pure silver. On the other hand, from the
viewpoint of flatness and durability of the silver-containing metal
layer, the silver-containing metal layer preferably contains metal
elements other than silver.
[0054] The total film thickness of the anchor region 7, the
silver-containing metal layer 4, and the cap region 9 in the
antireflection film is preferably 10 nm or less and more preferably
0.5 nm or more. Further, the total film thickness is preferably 2.0
nm or more, more preferably 2.5 nm or more, and particularly
preferably 3 nm or more. The total film thickness including the
anchor region 7, the silver-containing metal layer 4, and cap
region 9 in the antireflection film after production is a value
obtained by X-ray reflectance measurement. Specifically, the total
film thickness is a value obtained by measuring a signal near the
critical angle using RIGAKU RINT ULTIMA III (CuK.alpha.-ray, 40 kV,
40 mA), extracting a vibration component to be obtained and fitting
the vibration component. The film thickness of the
silver-containing metal layer 4 itself is preferably 6 nm or less
from the result of simulation (Example 7 or the like). Since the
silver-containing metal layer 4 is a film which is formed to be
very thin, actually, discontinuous regions or missing regions may
be formed in some cases.
[0055] In addition, the formed film surface is not a perfectly
smooth surface and is typically a surface having granular
unevenness. This means that as the grain size of crystal grains
(crystal grain size) forming the granular unevenness becomes
smaller, the smoothness becomes higher. In the present invention,
the crystal grain size obtained by X-ray diffraction measurement in
the silver-containing metal layer is less than 6.8 nm.
[0056] A vapor phase film formation method such as vacuum
deposition, plasma sputtering, electron cyclotron sputtering, or
ion plating is preferably used to form the silver-containing metal
layer 4.
[0057] The refractive index of the dielectric layer 5 is preferably
1.35 or more and 1.51 or less. The material for constituting the
dielectric layer 5 is not particularly limited. Examples thereof
include silicon oxide (SiO.sub.2), silicon oxynitride (SiON),
magnesium fluoride (MgF.sub.2), and sodium aluminum fluoride
(Na.sub.3AlF.sub.6). Particularly preferable is SiO.sub.2 or
MgF.sub.2. The refractive index can be changed to some extent by
controlling any of these compounds to have the constitutional
element ratio which is shifted from the compositional ratio of the
stoichiometric ratio or by forming a film by controlling the film
formation density.
[0058] The thickness of the dielectric layer 5 is preferably about
.lamda./4n in a case in which a target wavelength is .lamda. and
the refractive index of the dielectric layer is n. Specifically,
the thickness of the dielectric layer is about 70 nm to 100 nm.
[0059] The anchor region 7 is a region formed by alternation of an
anchor layer which is provided to smoothly form the
silver-containing metal layer after the interlayer 3 is laminated
and before the silver-containing metal layer 4 is laminated, is
formed of an anchor metal, and has a thickness of 0.2 nm to 2 nm
(refer to the production method described later) in the production
process, and is an interface region between the interlayer 3 and
the silver-containing metal layer 4. Here, the alternation means
that mixing with the constitutional elements of the interlayer and
the silver-containing metal layer or oxidation of a metal element
or the like occurs and the state of the anchor layer becomes
different from the state at the time of formation of the layer.
[0060] Similarly, the cap region 9 is an interface region between
the silver-containing metal layer 4 and the dielectric layer 5
including an oxide of the anchor metal obtained in such a manner
that the anchor metal constituting the anchor layer is made to pass
through the silver-containing metal layer 4 and is oxidized by
oxygen under an environment on the surface of the silver-containing
metal layer 4 in the production process.
[0061] After the anchor layer 6 is altered to the anchor region 7
and the cap region 9, there is a case where the total film
thickness of both regions 7 and 9 is increased with the oxidation
of the anchor metal by about two times compared to the film
thickness of the anchor layer 6.
[0062] Accordingly, the atoms present in the silver-containing
metal layer 4 and the interlayer 3 are mixed in the anchor region 7
in addition to the anchor metal and the oxide thereof, and the
atoms present in the silver-containing metal layer 4 and the
dielectric layer 5 are mixed in the cap region 9 in addition to the
anchor metal oxide. The anchor region 7 and the cap region 9 are
regions in which when the content of the anchor metal is measured
in the depth direction (lamination direction), the content is about
1 nm or less around a position showing the peak (the position in
the depth direction) in a line profile showing a change in the
content at the position in the depth direction (refer to FIG. 9).
In the line profile, two peaks are observed. Of the two peaks, one
closer to the substrate is the peak of the anchor region and the
other far from the substrate is the peak of the cap region. The
anchor metal content peak position can be calculated from the line
profile of, for example, TEM-EDX: (transmission electron microscope
(TEM)-energy dispersive X-ray spectroscopy (EDX)) (example of
device: HD-2700, manufactured by Hitachi High-Technologies
Corporation). In the line profile, the point where the signal of
the anchor metal is strong (maximum value) is calculated as the
peak position (for example, refer to FIG. 9 or the like).
[0063] The anchor metal has a surface energy that is less than the
surface energy of silver and greater than the surface energy of a
layer of the interlayer closest to the silver-containing metal
layer. In the present specification, the surface energy is defined
as a surface energy (surface tension) .gamma. calculated using
.gamma.=.gamma..sub.0+(t-t.sub.0)(d.gamma./dt) from Metal Data
Book, edited by The Japan Institute of Metals, version No. 4, p.
16.
[0064] Hereinafter, the surface energies of various metal elements
at room temperature calculated by the above method are
exemplified.
TABLE-US-00001 TABLE 1 Surface energy .gamma. Element (mN/m) Bi
395.22 Pb 507.26 Sn 558.49 In 567.844 Mg 778.1 Nd 778.91 Zn 848.98
Ge 857.34 Si 1045.05 Ag 1052.712 Al 1136.25 Mn 1333.2 Cu 1422.54 Au
1679.76 Pd 1835.94 Hf 2032.78 Ga 718 Ti 2081.6 Cr 2292 Ir 2317.983
Ni 2321.02 Co 2592.32 Fe 2612.39 Ta 2888 Mo 3024.6 W 3472.08
According to the above table, the surface energy of silver is 1053
mN/m. In contrast, for the layer of the interlayer closest to the
silver-containing metal layer (hereinafter, referred to as the
outermost layer of the interlayer), specifically, an oxide,
nitride, oxynitride or fluoride of a metal applicable to the layer
of low refractive index or the layer of high refractive index may
be used and these compounds generally have surface energy smaller
than the surface energy of the metal. For example, the surface
energies of SiO.sub.2, TiO.sub.2, and Ta.sub.2O.sub.5 are about 200
mN/m, 350 mN/m, and 280 mN/m, respectively.
[0065] In a case where an ultrathin film of silver having a large
surface energy (thickness: 6 nm or less) is directly formed on an
oxide or nitride film having a small surface energy, a case where
silver particles are bonded to each other is more stable than a
case where the silver is bonded with the oxide or nitride. Thus,
grain growth of the silver is promoted and it is difficult to form
a smooth ultrathin film. As the present inventors are conducting an
investigation to form a smooth ultrathin film, promoting the
bonding between the silver and the substrate using the anchor layer
is effective for suppressing the growth of crystal grains to obtain
a smooth ultrathin film of silver. Initially, although the physical
properties required for this anchor layer are not clear, it is
found that the surface energy of the anchor layer is an important
parameter to obtain a smooth ultrathin film. Specifically, for
example, since the surface energy of silver is 5 times or more
greater than the surface energy of SiO.sub.2 used for the
interlayer. Thus, it is found that, in order to reduce a difference
between the surface energies, the anchor layer having a surface
energy between the surface energy of the outermost layer of the
interlayer and the surface energy of silver is introduced so that a
smooth ultrathin film of silver can be obtained.
[0066] As the anchor metal, among the metal elements exemplified in
Table 1, bismuth (Bi), lead (Pb), tin (Sn), indium (In), magnesium
(Mg), zinc (Zn), gallium (Ga), germanium (Ge), and silicon (Si)
having a surface energy satisfying a range of about more than 200
mN/m and less than 1053 mN/m can be applied.
[0067] The surface energy of the anchor metal is preferably 350
mN/m or more and 1000 mN/m or less, and more preferably 500 mN/m or
more and 900 mN/m or less. Accordingly, Pb, Sn, In, Mg, Zn, Ga, and
Ge are preferable. According to the investigation of the present
inventors, from the viewpoint of suppressing an increase in
particle size of Ag, In, Ga, and Ge are preferable, and Ge is
particularly preferable. The anchor metal may not be a single metal
but may include two or more metals.
[0068] When the anchor layer is formed, an alloy layer formed of
two or more metals may be formed and when the anchor layer is
formed, a plurality of layers formed of a single metal may be
laminated. In a case where a plurality of layers are laminated, it
is preferable that the surface energy of layer close to the
outermost layer of the interlayer is small and the layers are
laminated so that the surface energy becomes larger in the order of
lamination.
[0069] On the other hand, there is a concern of lowering of
transparency due to the metal constituting such an anchor layer,
but it is found that transparency is improved by effectively
oxidizing the anchor metal to form a metal oxide.
[0070] Although it is described in JP2006-184849A that as the
protective layer for protecting the metal thin film from corrosion,
a metal oxide may be provided for the upper and lower layers of the
metal thin film, in a case where the underlayer when the
silver-containing metal layer is formed is an oxide layer, as
already described above, a homogeneous metal ultrathin film cannot
be formed. On the other hand, in a method of producing the
antireflection film according to the present invention, the anchor
layer formed of the anchor metal is not oxidized and the
silver-containing metal layer is formed on the anchor layer. Thus,
it is possible to sufficiently secure flatness. Since the anchor
layer is oxidized after sufficient flatness and adhesiveness are
secured, a metal ultrathin film achieving both high flatness and
high transparency can be formed.
[0071] There is a case where an oxidized anchor metal (anchor metal
oxide) and an unoxidized anchor metal are mixed in the anchor
region. However, it is desirable that the content of the anchor
metal oxide is larger than the content of the unoxidized anchor
metal, and it is particularly preferable that the anchor metal
included in the anchor region is fully oxidized. The magnitude
relationship between the content of the oxide of the anchor metal
and the content of the unoxidized anchor metal in the anchor region
can be confirmed based on the signal intensity ratio in measurement
by X-ray photoelectron spectroscopy (XPS).
[0072] On the other hand, it is preferable that the anchor metal
included in the cap region is fully oxidized to form an anchor
metal oxide.
[0073] The cap region is considered to have an effect of preventing
silver from aggregating and growing into a granular form at the
time of annealing. In the production process, in a stage in which
the anchor layer and the silver-containing metal layer are
sequentially formed, the anchor metal starts to move to the cap
region and in this state, oxidation of the anchor metal moved to
the surface occurs by exposure to the ambient air.
[0074] It is considered that the anchor metal becomes stable by
becoming an oxide, and cap performance such as silver migration
suppression, aggregation suppression, long-term stability, water
resistance and moisture resistance is improved. The most part of
the anchor metal of the cap region is oxidized by annealing in the
presence of oxygen. At this time, it is preferable that 80% or more
of the anchor metal included in the cap region is oxidized and it
is more preferable that all of the anchor metal in the cap region
is oxidized to form an anchor metal oxide. For example, in a case
where the anchor metal is Ge, it is preferable to satisfy
Ge/O.ltoreq.1/1.8 and it is particularly preferable to satisfy
Ge/O=1/2.
[0075] By providing the anchor region and the cap region as
described above, an ultrathin silver film structure achieving both
high flatness and high transparency can be realized. The
antireflection film according to the embodiment of the present
invention may include other layers such as a protective layer
having a function of protection for suppressing oxidation of the
silver-containing metal layer, in addition to the above-described
respective layers. In addition, in the film formation of each layer
constituting the antireflection film according to the embodiment of
the present invention, in a case where an ultrathin layer of nm
order is formed, it is difficult to form a uniform film, and in
reality, an uneven film is formed or parts (sea) not partially
formed into a sea-island state are formed. However, the present
invention includes such forms.
[0076] A method of producing an antireflection film for obtaining a
structure including the anchor region and the cap region for
realizing the effect of the present invention will be described.
FIG. 2 is a diagram showing a production step.
[0077] The interlayer 3 is formed on the substrate 2 (Step 1), then
a metal in a metal oxide included in the anchor region and the cap
region is formed into a layer as the anchor layer 6, and further,
the silver-containing metal layer 4 is formed (Step 2). The anchor
layer 6 and the silver-containing metal layer 4 are formed in the
atmosphere in which oxygen does not exist. The film thickness of
the anchor layer is preferably about 0.2 nm to 2.0 nm.
[0078] Since a part of the anchor metal constituting the anchor
layer is moved to the surface of the silver-containing metal layer
4 in the production process in the antireflection film as already
described above, the anchor layer is altered into the anchor region
and the thickness is greatly changed. The movement (diffusion) of
the anchor metal starts to occur immediately after the
silver-containing metal layer 4 is formed.
[0079] Thereafter, the substrate 2 in which the interlayer 3, the
anchor layer 6, and the silver-containing metal layer 4 are
laminated in order is exposed to the ambient air and annealing is
performed in the ambient air (Step 3). The annealing temperature is
preferably 100.degree. C. to 400.degree. C. and the annealing time
is preferably about 1 minute to 2 hours. When the annealing is
started, the anchor metal in the anchor layer 6 already moves
through the silver-containing metal layer 4 and a precursor region
9a of the cap region is being formed on the surface of the
silver-containing metal layer 4. On the other hand, the anchor
layer 6 becomes a region 7a in the middle of alternation into the
anchor region.
[0080] In the anchor metal which has started to move after the film
formation, the anchor metal moved to the surface of the
silver-containing metal layer 4 starts to be oxidized in a stage in
which the substrate 2 is exposed to the ambient air. Then, the
diffusion or oxidation of the anchor metal is promoted by annealing
and after the annealing treatment, the anchor layer 6 is altered
into the anchor region 7 and the anchor metal which has passed
through the silver-containing metal layer 4 and moved to the
surface of the laminate is oxidized to form a metal oxide. Thus,
the cap region 9 including the metal oxide is formed (Step 4).
[0081] Thereafter, the dielectric layer 5 is formed on the cap
region 9 which is the outermost surface of the laminate (Step
5).
[0082] Through the above steps, the antireflection film 1 of the
embodiment shown in FIG. 1 can be prepared.
[0083] The antireflection film according to the embodiment of the
present invention can be applied to the surface of various optical
members. Since the antireflection film can be applied to a lens
surface having a high refractive index, for example, the
antireflection film is suitably used for the outermost surface of a
known zoom lens described in JP2011-186417A.
[0084] An embodiment of an optical system constituted by a group
lens including the antireflection film 1 of the above-described
first embodiment will be described.
[0085] (A), (B), and (C) of FIG. 3 show configuration examples of a
zoom lens which is an embodiment of the optical system according to
the embodiment of the present invention. (A) of FIG. 3 corresponds
to an optical system arrangement at a wide angle end (shortest
focal length state), (B) of FIG. 3 corresponds to an optical system
arrangement in a middle area (intermediate focal length state), and
(C) of FIG. 3 corresponds to an optical system arrangement at a
telephoto end (longest focal length state).
[0086] The zoom lens includes a first lens group G1, a second lens
group G2, a third lens group G3, a fourth lens group G4, and a
fifth lens group G5 in order from an object along an optical axis
Z1. An optical aperture stop S1 is preferably arranged between the
second lens group G2 and the third lens group G3 in the vicinity of
the third lens group G3 on the side close to the object. Each of
the lens groups G1 to G5 includes one or a plurality of lenses Lij.
The reference symbol Lij denotes a j-th lens with the reference
symbol affixed such that a lens arranged to be closest to the
object in an i-th lens group is made into the first side and the
reference symbol is gradually increased toward an image forming
side.
[0087] The zoom lens can be mounted in an information portable
terminal as well as imaging devices, for example, a video camera,
and a digital camera. On the imaging side of the zoom lens, members
are arranged according to the configuration of an imaging portion
of a camera in which the lens is to be mounted. For example, an
imaging element 100 such as a charge coupled device (CCD) or a
complementary metal oxide semiconductor (CMOS) is arranged on an
image forming surface (imaging surface) of the zoom lens. Various
optical members GC may be arranged between the final lens group
(fifth lens group G5) and the imaging element 100 according to the
configuration of the camera side in which the lens is mounted.
[0088] The zoom lens is configured such that the magnification is
changed by chaining the gaps between the individual groups by
moving at least the first lens group G1, the third lens group G3,
and the fourth lens group G4 along the optical axis Z1. In
addition, the fourth lens group G4 may be moved at focusing. It is
preferable that the fifth lens group G5 is always fixed in
magnification change and at focusing. The aperture stop S1 is moved
together with the third lens group G3, for example. More
specifically, as the magnification changes from the wide angle end
to the middle area and further to the telephoto end, each lens
group and the aperture stop S1 is moved, for example, from the
state of (A) of FIG. 3 to the state of (B) of FIG. 3 and further to
the state of (C) of FIG. 3 along the locus indicated the solid line
in the drawing.
[0089] The antireflection film 1 is provided on the outermost
surfaces of the zoom lens of the outer surface (the surface close
to the object) of a lens L11 of the first lens group G1 and a lens
L51 of the fifth lens group G5 which is the final lens group. The
antireflection film 1 may be provided other lens surfaces in the
same manner.
[0090] Since the antireflection film 1 of the embodiment has high
mechanical strength, the antireflection film can be provided on the
outermost surface of the zoom lens which may be touched by a user
and thus a zoom lens having very high antireflection performance
can be formed.
[0091] In addition, in the antireflection film having a fine uneven
structure, fluctuations in the refractive index are present in
addition to the uneven structure and thus there is a concern of
scattering occurring due to the fluctuations in the refractive
index. However, since almost no fluctuations the in refractive
index are present in the antireflection film according to the
embodiment of the present invention having an uneven structure,
scattering hardly occurs. In the antireflection film in a camera
lens, scattering causes the occurrence of flare and thus a contrast
in an image is lowered. Thus, scattering is suppressed by providing
the antireflection film according to the embodiment of the present
invention, and as a result, it is possible to prevent a contrast in
an image from being lowered.
EXAMPLES
[0092] Hereinafter, a structure of main portions of the present
invention will be described using specific examples.
[0093] First, samples of Examples and Comparative Examples in which
an anchor region, a silver-containing metal layer, and a cap region
were provided on a glass substrate were prepared. The results of
evaluation of the transparency and the smoothness of the
silver-containing metal layer thereof will be described.
[0094] <Method of Preparing Sample>
[0095] An anchor layer formed of an anchor metal shown in Table 2
was formed on a glass substrate (SiO.sub.2 substrate). The film was
formed under the following conditions using a sputtering apparatus
(CFS-8EP) manufactured by Shibaura Mechatronics Co., Ltd.
[0096] Direct current (DC) input power=20 W
[0097] Ar: 20 sccm, Depo pressure (film formation pressure): 0.45
Pa
[0098] Film formation temperature: room temperature
[0099] A silver-containing metal layer was formed without exposure
to the ambient air subsequently after the anchor layer was formed.
Here, a silver film was formed as the silver-containing metal
layer. The film formation conditions are as follows.
[0100] DC input power=80 W
[0101] Ar: 15 sccm, Depo pressure: 0.27 Pa
[0102] Film formation temperature: room temperature
[0103] The anchor layer was formed at a thickness of 0.68 nm and
the silver film was formed at a thickness of 4 nm (the film
thickness herein is a design film thickness). The design film
thickness at the time of film formation means a film thickness
formed by obtaining the time required for forming the design film
thickness from the sputtering time in a case where 20 nm films were
respectively formed on the glass substrate under the same film
formation conditions and performing film formation during that
time.
[0104] Thereafter, the samples of each of Examples and Comparative
Examples were respectively annealed at the annealing temperature
and in the atmosphere shown in Table 2. The "Air" in Table 2 means
that annealing is performed in the ambient air and "Vac" means that
annealing is performed in vacuum without exposure to the ambient
air.
[0105] The samples of Examples and Comparative Examples obtained as
described above were subjected to the following measurements.
[0106] <Ratio Between Metal Region and Metal Oxide Region in
Anchor Region>
[0107] Evaluation was performed by X-ray photoelectron spectroscopy
(XPS). As the measurement device, Quantera SXM manufactured by
ULVAC-PHI, Inc. was used.
[0108] FIGS. 4 and 5 are graphs showing element distributions of
the sample in Example 1 in an element distribution depth direction
in a depth direction from the surface of the laminate to the glass
substrate before annealing and after annealing, which are obtained
by XPS. In FIGS. 4 and 5, the horizontal axis 0 is the position of
the surface of the laminate, and in order to make the distribution
of Ge easier to see, Ge is shown at a magnification of 3 times.
Therefore, the actual content of Ge is 1/3 of the value on the
vertical axis of the graph. FIGS. 6 and 7 show Ge3d spectra
(Dn:n=1, 2, 3 . . . ) of the sample in Example 1 obtained by XPS
and obtained at each position in the depth direction by drilling by
Ar.sup.+ sputtering in the depth direction from the surface of the
laminate to the substrate before annealing and after annealing at
the same time. In the drawings, data D.sub.1 is the data on the
laminate surface position, and as n becomes larger, the data
indicates the position closer to the substrate drilled by Ar.sup.+
sputtering in a direction perpendicular to the surface. In FIGS. 6
and 7, regarding the peak of GeO.sub.2 on the surface is slightly
shifted to the low bond energy side due to the effect of Ar.sup.+
sputtering. The data acquisition interval in the horizontal axis
(sputtering time) in FIGS. 4 and 5 the data acquisition interval
from the surface to the substrate in FIGS. 6 and 7 correspond to
each other.
[0109] By comparing FIG. 6 with FIG. 7, it is found that the peak
of GeO.sub.2 on the surface becomes large after annealing, while
the peak of Ge present before annealing is not present after
annealing. In addition, in the inside in the depth direction,
before annealing, the peak intensity of Ge is higher than the peak
intensity of GeO.sub.2, but after annealing, inversely, the peak
intensity of GeO.sub.2 is higher than the peak intensity of Ge. At
least from FIG. 7, it is possible to determine that the content of
GeO.sub.2 is larger than the content of Ge in the anchor region of
the sample in Example 1 (after annealing). Specifically, it is
considered that the seventh and eighth data from the surface in
FIG. 7 corresponds to the anchor region.
[0110] <Evaluation of Presence of Oxide Layer in Cap
Region>
[0111] The presence of the oxide of the anchor metal in the cap
region measured by XPS and a transmission electron microscope (TEM)
was evaluated by energy dispersive X-ray spectrometry (EDX) (FIGS.
6 and 7).
[0112] FIG. 8 is a bright-field-scanning transmission electron
microscope image (Bright-field-STEM image) of the sample in Example
1, and an EDX analysis portion is the region shown by the white
line near the center in FIG. 8. FIG. 9 is a graph showing the
distribution of the element to be analyzed in the depth direction
according to the EDX analysis result. As a transmission electron
microscope, HD-2700 manufactured by Hitachi High-Technologies
Corporation was used.
[0113] As described above, the presence of GeO.sub.2 in the anchor
region in Example 1 was confirmed from FIG. 7. On the other hand,
the compositional ratio at each position in the depth direction is
clear from the distribution of each element in the depth direction
shown in FIG. 9, and from the compositional ratio, it is possible
to calculate the existence probability of GeO.sub.2 and Ge.
[0114] In FIG. 9, the anchor region is near at the position of 9.8
nm (indicated by P in FIG. 9) where the horizontal axis Ge is a
peak. Since the anchor region is a region adjacent to the
substrate, Si is bled out. At this peak position, the compositional
ratio of Ge, Si, and O is Ge (12%), Si (12%), and O (48%) and thus
it is found that oxygen is present in the forms of SiO.sub.2 and
GeO.sub.2.
[0115] Regarding Examples 1, 2, and 5, the magnitude of the content
ratio of the oxide and the unoxidized anchor metal in the anchor
region and the presence of the oxide of the anchor metal in the cap
layer were confirmed.
[0116] <Evaluation of Transparency>
[0117] The absorbance of light having a wavelength of 550 nm was
measured with a spectrophotometer. As the absorbance becomes lower,
the permeability becomes higher. As long as the absorbance is
approximately 10% or less, the film is a practically acceptable
level. Specifically, measurement was performed at a scan speed of
600 nm/min in a range of 300 nm to 1200 nm using HITACHI U-4000,
and the measured value at a wavelength of 550 nm was extracted.
[0118] <Evaluation of Flatness>
[0119] The crystal grain size of the silver particle in the silver
film was calculated by X-ray diffraction (XRD) measurement. For
evaluating the crystallinity of the very thin film, specifically,
grazing incidence X-ray diffraction (GIXRD) which is measurement
for a thin film with the incidence angle fixed near the critical
angle was used. An X-ray diffraction chart was obtained by GIXRD
and the crystal grain size was calculated using the Scherrer
equation from the half-width of the (111) plane peak of silver near
a diffraction angle 2.theta.=38.degree. generated in the X-ray
diffraction chart. The smaller the crystal grain size of the silver
particle is, the more preferable it is. However, the crystal grain
size is practically preferably 6 nm or less. The area of the X-ray
irradiation region by GIXRD is 1 cm.times.1 cm and the particle
size calculated based on the Scherrer equation is the average value
of the X-ray irradiation region.
[0120] <Film Thickness Measurement>
[0121] The film thickness was calculated by measurement of X-ray
reflectivity (XRR). The film thickness herein includes the cap
region, the silver film, and the anchor region.
[0122] In all of Examples and Comparative Examples, as already
described above, film formation is performed such that the design
film thickness of the silver film is 4 nm and the design film
thickness of the anchor layer is 0.68 nm. However, the film
thickness of the silver film after sample preparation changes
depending on preparation conditions such as the kind of metal of
the anchor layer, and annealing temperature. By fitting the
vibration component of XRR signal of the obtained film (sample),
the film thickness including the silver film, the anchor region,
and the cap region was calculated. As already described above,
considering that the anchor region and the cap region are very thin
and have a thickness of about 1 nm or less and the anchor metal is
diffused over the whole area of the silver film and the interface
region with SiO.sub.2, the film is considered to be constituted of
the SiO.sub.2 substrate and the silver film and fitting is
performed.
[0123] Table 2 collectively shows preparation conditions and
measurement (evaluation) results of the samples of Examples 1 to 6
and Comparative Examples 1 to 4 prepared and evaluated by the above
methods.
TABLE-US-00002 TABLE 2 Measurement (evaluation) results Film
Preparation Conditions thickness by Particle Anchor Annealing XRR
Anchor Absorbance size by metal temperature Atmosphere measurement
region @ 550 nm XRD Example 1 Ge 300.degree. C. Air 4.86 nm
GeO.sub.2 > 3.40% 3.9 nm Ge Example 2 Sn 300.degree. C. Air 4.92
nm SnO.sub.2 > 8.30% 4.8 nm Sn Example 3 Zn 300.degree. C. Air
5.12 nm -- 9.23% 5.3 nm Example 4 Ge 100.degree. C. Air 4.86 nm
GeO.sub.2 < 8.20% 4.1 nm Ge Example 5 In 300.degree. C. Air 4.93
nm -- 7.56% 3.8 nm Example 6 Ga 300.degree. C. Air 4.88 nm -- 9.87%
4.3 nm Comparative Ge 300.degree. C. Vac 4.95 nm Ge > 11.20%
13.2 nm Example 1 GeO.sub.2 Comparative Cr 300.degree. C. Air 5.04
nm -- >20% 11.2 nm Example 2 Comparative mo 300.degree. C. Air
5.32 nm -- >20% 12.3 nm Example 3 Comparative Al 300.degree. C.
Air 4.75 nm -- -- 6.8 nm Example 4
[0124] In Table 2, the part indicated by "-"indicates that the
evaluation is not performed.
[0125] As shown in Table 2, in Examples 1 to 6 in which the anchor
metal satisfying the conditions of the present invention was used
and annealing was performed in an oxygen-containing atmosphere, as
compared with Comparative Examples, it is found that the particle
size of the silver particles is suppressed and the smoothness is
high. Further, in Examples 1, 2, and 4 in which the transparency
was evaluated at the same time, the absorbance was lower than those
of Comparative Examples. It is found from the absorbances of
Examples 1 and 5 that as the ratio of the oxide in the anchor
region increases, the absorbance decreases. It is considered that
the oxidation of the anchor metal is promoted by adjusting the
annealing temperature and time, so that the transparency can be
improved. On the other hand, it is considered that while the same
anchor metal as in Example 1 was used in Comparative Example 1,
annealing was performed in an environment where oxygen does not
exist, and thus, the transparency could not be sufficiently
improved. Further, it is considered that since the oxidization of
the anchor metal in the cap region was not sufficient, aggregation
of silver occurred at the time of annealing and the particle size
of silver was increased. That is, it is considered that the anchor
metal in the cap region has to be sufficiently oxidized to form an
oxide in order to attain sufficient smoothness of the silver
film.
[0126] In the antireflection film according to the embodiment of
the present invention, examples of the specific layer structure
contributing to antireflection performance will be described. The
followings are simulation results of the film thickness obtained by
optimizing the film thickness using Essential Macleod (manufactured
by Thin Film Center Inc.) and the wavelength dependence of the
reflectance.
Example 7
[0127] A layer structure from a substrate to air as a medium was
set as shown in Table 3.
[0128] Assuming FDS90 (manufactured by HOYA Corporation) as the
substrate, the refractive index was set to 1.86814. Each interlayer
respectively adopted a four-layer structure (Example 7-1) in which
a SiO.sub.2 layer having a refractive index of 1.46235 as a layer
of low refractive index and a Nb.sub.2O.sub.5 layer having a
refractive index of 2.3955 as a layer of high refractive index were
alternately laminated, a five-layer structure (Example 7-2), a
six-layer structure (Example 7-3), a seven-layer structure (Example
7-4), an eight-layer structure (Example 7-5), a twelve-layer
structure (Example 7-6), and a sixteen-layer structure (Example
7-7), the silver-containing metal layer was formed of Ag, and the
dielectric layer was formed of MgF.sub.2. Then, the film thickness
of each example was optimized so as to minimize the
reflectance.
TABLE-US-00003 TABLE 3 Example 7 Example 7-1 Example 7-2 Example
7-3 Example 7-4 Example 7-5 Example 7-6 Example 7-7 Physical film
Physical film Physical film Physical film Physical film Physical
film Physical film Constituent Refractive thickness thickness
thickness thickness thickness thickness thickness Layer material
index (nm) (nm) (nm) (nm) (nm) (nm) (nm) Medium Air 1 -- -- -- --
-- -- -- Dielectric MgF.sub.2 1.3857 92.94 92.79 91.07 91 90.54
90.58 89.55 layer Metal layer Ag 0.05 3.07 3.2 4.01 4.19 4.16 4.32
4.53 Interlayer 1 Nb.sub.2O.sub.5 2.3955 22 22.11 18.88 18.4 17.52
17.56 16.34 Interlayer 2 SiO.sub.2 1.46235 47.22 48.98 73.06 83.53
82.92 94.22 118.14 Interlayer 3 Nb.sub.2O.sub.5 2.3955 17.85 18.46
9.78 8.03 6 5.96 5.35 Interlayer 4 SiO.sub.2 1.46235 25.5 35.63
65.78 72.05 71.83 74.88 63.99 Interlayer 5 Nb.sub.2O.sub.5 2.3955
-- 5.62 13.57 16.63 10.53 16.3 20.98 Interlayer 6 SiO.sub.2 1.46235
-- -- 22.38 35.32 28.46 30.24 31.57 Interlayer 7 Nb.sub.2O.sub.5
2.3955 -- -- -- 8.39 8.61 4.72 9.43 Interlayer 8 SiO.sub.2 1.46235
-- -- -- -- 11.54 10.33 9.66 Interlayer 9 Nb.sub.2O.sub.5 2.3955 --
-- -- -- -- 12.53 19.42 Interlayer 10 SiO.sub.2 1.46235 -- -- -- --
-- 15.66 20.41 Interlayer 11 Nb.sub.2O.sub.5 2.3955 -- -- -- -- --
7.54 8.54 Interlayer 12 SiO.sub.2 1.46235 -- -- -- -- -- 4.51 9.3
Interlayer 13 Nb.sub.2O.sub.5 2.3955 -- -- -- -- -- -- 9.67
Interlayer 14 SiO.sub.2 1.46235 -- -- -- -- -- -- 14.14 Interlayer
15 Nb.sub.2O.sub.5 2.3955 -- -- -- -- -- -- 9.47 Interlayer 16
SiO.sub.2 1.46235 -- -- -- -- -- -- 5.69 Substrate FDS90 1.86814 --
-- -- -- -- -- --
[0129] The simulation results of the reflectance of each
antireflection film of Example 7 with respect to light incident at
a light incidence angle of 0.degree. (light vertically incident to
the surface) are shown in FIG. 10. The numbers in the parentheses
after each example shown in the explanatory note refer to the total
number of interlayers. As shown in FIG. 10, the antireflection
films of Examples 7-1 and 7-2 exhibited a reflectance of 0.2% or
less over a wide wavelength range of 400 nm to 780 nm, and the
antireflection films of Examples 7-3, 7-4, 7-5, 7-6, and 7-7
exhibited a reflectance of 0.2% or less over a wider wavelength
range of 400 nm to 800 nm and exhibited a reflectance of 0.1% or
less in a wavelength range of 400 nm to 780 nm. Very satisfactory
antireflection properties were obtained.
Preparation Examples of Silver-Containing Metal Film
[0130] In a case where each antireflection film of Example 7
obtained in the above-described simulation was actually prepared,
as already described above, antireflection properties change
greatly depending on the formation accuracy of the metal film
particularly including Ag. The cause of the deviation from the
simulation will be described in detail below.
Preparation Example 1
[0131] A film formed of pure silver was formed at a thickness of 5
nm on the substrate by an electron beam vapor deposition method
using EVD-1501 manufactured by Canon Anelva Corporation and the
reflection spectrum of the film formed of pure silver (silver film)
was measured by using a reflection film thickness spectrometer
FE3000 manufactured by Otsuka Electronics Co., Ltd.
Preparation Example 2
[0132] A silver alloy film was formed was formed at a thickness of
5 nm on the substrate by a sputtering method using GDO2
(manufactured by KOBELCO research institute), which is a silver
alloy target (Ag--0.7% Nd--0.9% Cu: hereinafter, referred to as
ANC), as a target, and the reflection spectrum of the film was
measured by using a reflection film thickness spectrometer FE3000
manufactured by Otsuka Electronics Co., Ltd.
[0133] FIG. 11 shows the reflection spectra of the silver film (Ag)
in Preparation Example 1 and the silver alloy film (ANC) in
Preparation Example 2 together with a calculated value (simulation)
of a pure silver film of a thickness of 5 nm.
[0134] As shown in FIG. 11, the reflection spectrum of the film of
Preparation Example 1 greatly deviated from the calculated value of
a pure silver film of a thickness of 5 nm while the reflection
spectrum of the film in Preparation Example 2 was consistent with
the calculated value with a very high accuracy. Since the contents
of metals other than silver in the ANC are small, the contribution
to reflectance by components other than silver can be
neglected.
[0135] The surface of each film in Preparation Examples 1 and 2 was
evaluated using a scanning electron microscope (SEM) and an atomic
force microscope (AFM).
[0136] FIG. 12 is an SEM image of Preparation Example 1 (Ag) and
FIG. 13 is an SEM image of Preparation Example 2 (ANC).
[0137] As shown in FIG. 12, the silver film in Preparation Example
1 does not have uniform film thickness and grows into a granular
form. Since the silver grows into a granular form in this manner,
it is considered that plasmon resonance occurs due to the incidence
ray, resulting in a reflection spectrum whose reflectance is
significantly different from the calculated value. On the other
hand, as shown in FIG. 13, an ANC alloy film having a very small
particle size and high flatness compared to the silver film in
Preparation Example 1 is obtained.
[0138] FIGS. 11 to 13 shows that as the silver-containing metal
layer, as in Preparation Example 2, in a case of using a film
having a smaller particle size and higher smoothness, an
antireflection film having properties closer to the wavelength
dependence of the reflectance obtained in the simulation can be
obtained. The particle size in the silver film in Preparation
Example 1 shown in FIG. 12 is about 15 to 20 nm, but the particle
size of the ANC alloy film in Preparation Example 2 shown in FIG.
13 is 6.3 nm. Since the anchor layer is not introduced into the
film shown in FIG. 13, the flatness is improved but is not
sufficient.
[0139] That is, it is considered that by applying the silver film
having high flatness as in the samples in Examples 1 to 6 described
above to the layer structure of the antireflection film in Example
7, an antireflection film having properties closer to the
wavelength dependence of the reflectance obtained in the simulation
can be obtained. Since the anchor region and the cap region are
very thin and have a thickness of about 1 nm, the regions hardly
contribute to the antireflection function and the reflectance of
the simulation shown in Example 7 above is hardly changed.
EXPLANATION OF REFERENCES
[0140] 1 antireflection film
[0141] 2: substrate
[0142] 3: interlayer
[0143] 4: silver-containing metal layer
[0144] 5: dielectric layer
[0145] 6: anchor layer
[0146] 7: anchor region
[0147] 7a: region in the middle of alternation into anchor
region
[0148] 9: cap region
[0149] 9a: precursor region of cap region
[0150] 10: optical element
[0151] 11: layer of high refractive index
[0152] 12: layer of low refractive index
[0153] 100: imaging element
[0154] G1 to G5: lens group
[0155] GC: optical member
[0156] L11 to L51: lens
[0157] S1: aperture stop
[0158] Z1: optical axis
* * * * *